1. Field of the Invention
The present invention relates to an image data creating method and apparatus, and more specifically to an image data creating method and apparatus for creating image data representing a single image by combining a plurality of image data representing a plurality of image portions sharing a common region.
2. Description of the Related Art
A system for reading out an original is known, in which a linear detecting section comprising a linear sensor having a plurality of light receiving sections disposed linearly in the main scanning direction is moved over the original in the sub-scanning direction. In reading out a large-sized original with the system described above, a wide linear detecting section comprising a long linear sensor is used, which is formed of a plurality of shorter linear sensors disposed in the main scanning direction such that their ends are overlapped with each other to act collectively as a long single linear sensor, since it is difficult to realize such a long seamless sensor because of the constraints imposed by the manufacturing process.
When a large-sized original is read out by the linear detecting means formed in the manner described above, a single position on the large-sized original is detected by the light receiving sections disposed on the end portion of each of the mutually overlapped linear sensors in duplicate, and the image data (also referred to as “image data group”),representing a portion of the large-sized original sharing the same position is obtained by each of the linear sensors, and then these image data groups are combined to create the image data representing a complete large-sized original.
As for the method of creating image data representing a complete large-sized original by combining a plurality of image data groups, each representing a portion of the large-sized original, a method in which image data groups obtained by respective sensors are simply linked together by delimiting each of the image data groups, and an improved technique of this method in which a plurality of image data representing the same position on the large-sized original detected by the light receiving sections disposed on the mutually overlapped end of each of the sensors are averaged such that the image data obtained by a light receiving section located closer to the end of the sensor are allocated a smaller weighting factor to obtain the image data of the respective positions, and the image data representing the complete large-sized original are created by using these data are described, for example, in Japanese Unexamined Patent Publication No. 2002-57860, and U.S. Pat. No. 6,348,981. Here, the region represented by the image data obtained through the weighted averaging in the image of the complete large-sized original is a strip-like region extending in the sub-scanning direction.
The weighted averaging method described above, however, has a drawback that streaks may appear along the strip-like region due to the difference in noise element contained in the strip-like region where the weighted averaging is implemented, and the image region other than the strip-like region where no weighted averaging is implemented, causing quality degradation in the overall image of the large-sized original.
The streaks appearing along the strip-like region are due to the difference in the texture of the image caused by the difference in noise element contained in the image data representing the strip-like region and the image data where no weighed averaging is implemented, which has resulted from the reduced noise element in the strip-like region through the averaging effect of the weighted averaging.
The problem described above is not limited to the case in which a plurality of linear sensors are moved over an original to obtain the image data, but common to the methods in which an arithmetic operation, such as the weighted averaging, is implemented on a plurality of image data groups, each representing a portion of image that shares a common region, in order to combine them to create image data representing a single complete image.